This invention relates to modulated infrared countermeasuring of heat seeking missiles and more particularly and generically to a method of countermeasuring in which spatial modulation is provided by the rotation of an infrared (IR) beam in a 360xc2x0 azimuth.
The modulation of infrared radiation, due to its long wavelength, has not been accomplished easily in the past. Problems in modulation of infrared energy include those of unwanted refraction due to the long wavelengths as well as absorption of the energy by the apparatus utilized in the modulation technique. Absorbed energy is reradiated in a diffused pattern thereby in many instances degrading the modulation. Additional problems center around materials which can withstand the infrared radiation while the same time being sufficiently light weight and structurally stable enough to withstand cyclic motion normally employed in the production of a modulated beam. It will be appreciated that when IR sources include heated elements, modulation of the energy to the element is ineffective to cause modulation of the radiation from the element due to the long heating and cooling cycles inherent with the IR sources in which elements are heated.
One of the most important applications of modulated infrared sources is in the area of infrared countermeasures. In this application, the modulated infrared source is employed to render ineffective heat seeking missiles which typically home in on the heat generated by the engines which propel the target at which the missile is aimed. These engines include internal combustion engines, jet engines, rocket engines or the like.
In general, it is the purpose of the infrared countermeasure device to produce a modulated infrared signal of sufficiently high intensity to mask the infrared output from the above mentioned engines. Modulated infrared sources exist in the prior art which employ IR sources with temporal modulators. This invokes the so-called xe2x80x9cchopperxe2x80x9d technique, in which apertures spaced from the source are sequentially covered and uncovered in a shutter technique. However, in these sources when the apertures are covered energy radiated from the IR source is either absorbed by the occluding member or reflected back into the source at a non-optimum angle such that this energy is lost. Where energy for the IR source is virtually unlimited, such as is the case when fuel is burned for the production of infrared radiation, temporal modulation techniques work well. Temporal modulation of electrically powered sources also works quite well where sufficiently large amounts of electrical power are available as in jet powered fighter aircraft. However, when the IR source must depend for its energy on electrical power which is critically limited, to overcome radiation from the target""s engines it is desireable that as much of the energy from the IR source as possible be utilized in order that the infrared source radiate sufficient energy to blanket or mask the infrared energy from the target""s engine.
Moreover, to provide omnidirectional coverage the infrared source must be omnidirectional so as to be able to countermeasure heat seeking missiles coming in from any direction. In the prior art omnidirectional coverage has been obtained by the provision of a large number of apertures about the IR source. The modulation is obtained by the rotation of a cylindrically shaped mask in front of the apertures. While these systems are effective where unlimited power is available, the provision of temporal modulation presents a problem of efficiency which can be critical in many applications because the radiation from the source may be blanketed or masked by the radiation from the target.
The above problems are solved by the subject invention in which close to 100% of the infrared energy is coupled onto into space by xe2x80x9cspatial modulationxe2x80x9d. The term xe2x80x9cspatial modulationxe2x80x9d as used herein refers to the formation of an infrared beam in which the infrared beam is swept past a point in space removed from the infrared source a number of times per second, corresponding to the frequency of the modulation. In one embodiment of the subject invention this is accomplished by rotating the focusing optics about a stationary infrared source at an rpm commensurate with the modulation frequency desired. Alternatively the entire source can be rotated or reciprocated to produce a sweeping beam.
It is therefore an object of this invention to provide an improved countermeasure method.
It is another object of this invention to provide a method including a spatially modulated infrared source for countermeasuring heat seeking missiles.
It is a further object of this invention to provide a method of modulating an infrared source by the moving of focusing optics relative to the infrared source.
It is a yet still further object of this invention to provide an IR modulation method involving a spatially modulated omnidirectional infrared radiation source.